key plastic mold and molding terms

Mold and Molding Terms You Should Understand

mold terms, molding glossary, plastic terms

Whether you’re a seasoned professional or new to mold procurement, understanding key plastic mold and molding terms is crucial. In this post, we’ll share a concise list of essential terms to empower you with the knowledge needed for informed decision-making. To begin, let’s explore the terminology every mold buyer should know to navigate the complexities of plastic molding successfully.

Key Plastic Mold and Molding Terms

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AMBIENT TEMPERATURE: Temperature of the medium surrounding an object. Used to denote prevailing room temperature.

ANTISTATIC AGENTS: Agents which, when added to the molding material or applied on the surface of the molded part, make it less conducting.

ARTIFICIAL AGING: The accelerated testing of plastic specimens to determine their changes in properties. Carried out over a short period of time, such tests are indicative of what may be expected of a material under service conditions over extended periods. Typical investigations include those for dimensional stability; the effect of immersion in water, chemicals and solvents; light stability; and resistance to fatigue.

BACK DRAFT: Reverse draft used in mold to prevent molded articles from drawing freely.

BACK PRESSURE: A pressure against the free flow of material during extruder running which causes the material to have a high mixing action. This pressure comes from the material resisting the forward movement of the material in the extruder or an externally controlled hydraulic pressure put against the movement of the extruder in a reciprocation screw machine to create this greater mixing action.

BACKING PLATE: In mold construction, a plate used as a support for the cavity blocks, guide pins, bushings, etc.

BANANA GATE: Curved shape that wraps over or under the part with a curved shape that will break away from the part like a tunnel gate.

BARREL: In injection molding, extrusion or bottle blowing equipment, it is the hollow tube in which the plastic material is gradually heated and melt ed and from which it is extruded.

BLOOM: A visible exudation or efflorescence on the surface of a plastic. Bloom can be caused by lubricant, plasticizer, etc.

BLOW PIN: A hollow pin which is inserted or made to contact the blowing mold so that the blowing media can be introduced into the parison or hollow form and expand it to conform to the mold cavity.

BLOW RATE: The speed or rate that the blowing air or media enters or the time required to expand the parison (tube) or form during the blow molding cycle.

BLOW-UP RATIO: The ratio of the mold cavity diameter to the diameter of the parison or hollow form to be blown up.

BLUEING OFF: The checking of the accuracy of mold cutoff surfaces by putting a thin coating of Prussian Blue on one-half and checking the blue transfer to the other half.

BLUSH: A term used to describe the tendency of a plastic to turn white or chalky in areas that are highly stressed.

BOSS: Projection on a plastic part designed to add strength, to facilitate alignment during assembly, to provide for fastening, etc.

BOTTOM PLATE: Part of the mold which contains the heel radius and the push-up.

BREATHING: The opening and dosing of a mold to allow gases to escape early in the molding cycle. Also called degassing.

BURNED: Showing evidence of thermal decomposition through some discoloration, distortion, or localized destruction of the surface of the plastic.

CASE HARDEN: To harden the surface of a piece of steel to a relatively shallow depth.

CAVITY: Depression in mold, which usually forms the outer surface of the molded part; depending on number of such depressions, molds are designated as a single cavity mold, a multi-cavity mold, or a family cavity mold.

CAVITY RETAINER PLATE: Plates in a mold which hold the cavities. These plates are at the mold parting line and usually contain the guide pins and bushings.

CENTER GATED MOLD: An injection or transfer mold wherein the cavity is filled with molding material through a sprue or gate directly into the center of the part.

CHALKING: Dry, chalk-like appearance or deposit on the surface of a plastic.

CHARGE: The measurement or weight of material used to load a mold at one time or during one cycle.

CLAMPING AREA: The largest rated molding area an injection or transfer press can hold closed under full molding pressure.

CLAMPING FORCE: In injection molding and in transfer molding, the pressure which is applied to the mold to keep it closed against the fluid pressure of the compressed molding material within the mold cavity (cavities) and the runner system.

CLAMPING PLATE: A plate fitted to a mold and used to fasten mold to a molding machine.

COINJECTION: Two or more plastic materials may be injected simultaneously or sequentially in a specially designed injection molding machine.

COLD SHOT: Incomplete parts which are formed while cycling a molding machine during heat up.

COLD SLUG: The first material to enter an injection mold; so-called because in passing through sprue orifice it is cooled below the effective molding temperature.

COLD SLUG WELL: Space provided directly opposite the sprue opening in an injection mold to trap the cold slug.

COLOR CONCENTRATE: A mixture of a measured amount of dye or pigment and a specific plastic mate rial base. A more precise color can be obtained using concentrates rather than using raw colors. Note: Care should be taken to verify that the color concentrate base is compatible with the plastic it is to be used to color. Color concentrate is normally used at 1-4% of the plastic material to be colored.

COMPRESSION MOLD: A mold which is open when the material is introduced and which shapes the mate rial by heat and by the pressure of closing: used in compression molding.

COMPRESSION MOLDING: A technique of thermoset molding in which the molding compound (generally preheated) is placed in the heated open mold cavity, mold is closed, under pressure (usually in a hydraulic press) causing the material to flow and completely fill the cavity, pressure being held until the material has cured.

COOLING CHANNELS: Channels or passageways located within the body of a mold through which a cooling medium can be circulated to control temperature on the mold surface. May also be used for heating a mold by circulating steam, hot oil or other heated fluid through channels as in molding of the thermosetting and some thermoplastic materials.

CORE: Male element in die which produced a hole or recess in a part.

CORE PIN: Pin used to mold a hole.

CORE PIN PLATE: Plate holding core pins.

CORE ROD: A rod used to form the internal configuration of an injection blow molded parison or preform.

CORING: (1) (molded part design) -The removal of excess material from the cross section of a molded part to attain a more uniform wall thickness. (2) The method of sizing and shaping a bottle opening by appropriate tools.

CREEP: The dimensional change with time of a mate rial under load, following the initial instantaneous elastic deformation. Creep at room temperature is some times called COLD FLOW.

CYCLE: The complete, repeating sequence of operations in a process or part of a process. In molding, the cycle time is the period, or elapsed time, between a certain point in one cycle and the same point in the next.

DAYLIGHT OPENING: Clearance between two platens of a press in the open position.

DEBOSS: An indent or cut in design (depressed design) or lettering of a surface.

DIAPHRAGM GATE: Gate used in molding annular or tubular articles. Gate forms a solid web across the opening of the part.

DIMENSIONAL STABILITY: Ability of a plastic part to retain the precise shape in which it was molded, fabricated or cast.

DISCOLORATION: Any change from the original color, often caused by overheating, light exposure, irradiation, or chemical attack.

DISHED: Showing a symmetrical distortion of a flat or curved section of a plastic object, so that as normally viewed, it appears concave, or more concave than intended.

DOMED: Showing a symmetrical distortion of a flat or curved section of a plastic object, so that, as normally viewed, it appears convex, or more convex than intend ed.

DOWEL: Pin used to maintain alignment between two or more parts of a mold.

DRAFT: The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

DUPLICATE CAVITY PLATE: Removable plate that retains cavities, used where two-plate operation is necessary for loading inserts, etc.

Dimension “E”: In blow molding, on a threaded bottle neck (finish), the measurement across the root of the threads.

Dimension “H”: In blow molding, (1) On a threaded bottle neck (finish), the measurement from the top of the finish to the point where diameter “I” extended parallel to the centerline intersects the shoulder of bead. (2) The inside height of the closure, measured from the bot tom of the closure in a line tangent to the threads of the closure and terminating at the inside top of the closure.

Dimension “W”: In blow molding, the width (vertical height) of the neck band on certain bottle finishes.

Dimension”I”: In blow molding, a specified minimum dimension inside the bottle neck that will allow sufficient clearance for filler tubes to enter the bottle neck.

Dimension”L”: In blow molding, measured from the top of the finish to the point where diameter “E” extended parallel to centerline intersects the bead.

Dimension”S”: In blow molding, locates the position of the bottle thread with respect to the top of the finish. It is a vertical distance from the top of the finish to the intersection of the finish wall and the top of the first part of the bottle where full depth contour exists.

Dimension”T”: In blow molding, the outside diameter of the thread helix on a bottle finish.

EJECTION: The removal of the finished part from the mold cavity by mechanical means.

EJECTOR PIN: A rod, pin or sleeve which pushes a molding off of a force or out of a cavity of a mold. It is attached to an ejector bar or plate which can be actuated by the ejector rod(s) or the press or by auxiliary hydraulic or air cylinders.

EJECTOR PIN RETAINER PLATE: Retainer plate into which ejector pins are assembled.

EJECTOR RETURN PINS: Projections that push the ejector assembly back as the mold closes; also called Safety Pin, and Position Pushbacks.

EJECTOR ROD: A rod or bar that actuates the ejector assembly when mold is opened.

ELASTIC DEFORMATION: The part of the deformation of an object under load which is recoverable when the load is removed.

ELECTROPLATING: Deposition of metals on certain plastics and mold for finish.

ELONGATION: he fractional increase in length of a material stressed in tension, before rupture.

EMBOSSING: Techniques used to create depressions of a specific pattern in plastics film and sheeting. Such embossing is in the form of surface patterns on mold ed part by the treatment of the mold surface by photoengraving or other process.

ENVIRONMENTAL STRESS CRACKING: The susceptibility of a thermoplastic article to crack or craze formation under the influence of certain chemicals or aging, or weather, and stress.

ETCH: To treat a mold with an acid, leaving parts of the mold which remain in relief to form the desired design on the bottle.

EXTRUSION: The plasticizing of a material in an EXTRUDER (barrel and screw or plunger assembly) and forcing of the molten material or EXTRUDATE through a die or into a mold. The initial part of the molding process.

EXTRUSION BLOW MOLDING: A type of blow molding where the parison is formed in open air by an extrusion process.

FAMILY MOLD: A multi-cavity mold wherein each of the cavities forms one of the component parts of the assembled finished object.

FAN GATE: A shallow gate somewhat wider than the runner from which it extends.

FILLER: An inert substance added to plastics for the purpose of improving physical properties or process ability, or to reduce cost of the material.

FIXTURE: Means of holding a part during a machine or other operation.

FLASH: Extra plastic attached to a molding along the parting line; under most conditions it would be objectionable and must be removed before the parts are acceptable.

FLASH GATE: Usually a long gate extending from a runner which runs parallel to an edge of a molded part along the flash or parting line of the mold.

FLASH LINE: A raised line appearing on the surface of a molding and formed at the junction of mold faces.

FLOW LINE: A mark on a molded piece made by the meeting of two flow fronts during molding.

FLOW MARKS: Wavy surface appearance on a mold ed object caused by improper flow of the material into the mold.

GATE: In injection and transfer molding, the orifice through which the melt enters the cavity.

GRIT BLASTED: A surface treatment of a mold in which steel grit or sand materials are blown to the walls of the cavity to produce a roughened surface. Air escape from mold is improved and special appearance of molded article is often obtained by this method.

GUIDE PINS: Devices that maintain proper alignment of force plug and cavity as mold closes.

GUSSET: A piece used to give strength or additional size in a particular location of an object.

HAZE: In plastics, defined as the percentage of incident light scattered by more than 2.5° through the plastic specimen. It measures the milkiness of the material (film or sheet). It is expressed in percentage (%). It is an important optical property to measure where true color and visibility are necessary.

HOT RUNNER MOLD: A thermoplastic injection mold in which the runners are insulated from the chilled cavities and remain hot so that the center of the runner never cools in normal cycle operation. Runners are not usually, ejected with the molded pieces. Called INSULATED RUNNER MOLDS when heating elements are not used in mold. Note: A HEATED MANIFOLD MOLD is a HOT RUNNER MOLD which is both heated and insulated and an INSULATED MOLD is a HOT RUNNER MOLD which does not contain heaters

INSERT: An integral part of a plastics molding, consisting of metal or other material, which may be molded into position or may be pressed into the molding after the molding is completed. Also, a removable or inter changeable component of the mold.

JETTING: Turbulent flow of plastic from an undersized gate or thin section into a thicker mold section, as opposed to laminar flow of material progressing radially from a gate to the extremities of the cavity. May also result from shooting material into a mold cavity where there is no core or immediate cavity wall to break up the flow of the material coming through the gate.

Knockout Pin: A device for knocking a cured piece from a mold. Also called Ejector Pin.

LIGHT RESISTANCE: The ability of a plastics material to resist fading after exposure to sunlight or ultraviolet light.

MANDREL: The inner portion of the extrusion blow molder die head which is used to adjust parison wall thickness. Also called DIE PIN.

MOVABLE PLATEN: The moving platen of an injection or compression molding machine to which half of the mold is secured during operation. This platen is moved either by a hydraulic ram or a toggle mechanism.

MULTI-CAVITY MOLD: A mold having more than one cavity or impression for forming finished items at one machine cycle.

NECKING: The localized reduction of cross-section al area of an object.

OLEFIN PLASTICS: Plastics produced from olefins (POLYOLEFINS). Examples are polyethylene and polypropylene.

ORIENTATION: The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure. Can be accomplished by cold drawing or stretching during fabrication.

OUT-OF-ROUND: Non-uniform radius or diameter.

PARALLELS: The support spacers placed between the mold and press platen or damping plate. Also called RISERS or SUPPORT FILLERS.

PARISON: The hollow tube of thermoplastic material which is pinched at one or both ends and inflated in a mold to make a hollow part, i.e. Blow Molding.

PARTING LINE: (1)The points in the mold where two or more metal surfaces meet creating a shut off. (2) Mark on a molding or casting where halves of mold met in dosing.

PINPOINT GATE: A restricted orifice through which molten plastic flows into a mold cavity. Also called RESTRICTED GATE.

PLASTIC DEFORMATION: The deformation of a material under load that is not recoverable after the load is removed.

PLASTIC MEMORY: A phenomenon of plastics to return, in some degree, to its original form upon heating.

PLASTICIZE: To make a material soft and moldable with the addition of heat and/or pressure or a plasticizer.

PLASTICIZER: Chemical added to a plastic to make it soften and more flexible.

PLATENS: The mounting plates of a press to which the entire mold assembly is bolted.

PLUNGER: The part of a transfer or injection press that applies pressure on the un-melted plastic material to push it into the chamber, which in turn forces plastic melt at the front of the chamber out through the nozzle.

PREFORM: A pill, tablet, or biscuit used in thermoset molding. Material measured by volume, the bulk factor of powder reduced by pressure all in the interest of efficiency and accuracy.

PROTOTYPE MOLD: A simplified mold construction often made from a light metal casting alloy or from an epoxy resin in order to obtain information for the final mold and/or part design.

RECYCLED PLASTICS: A plastic material prepared from previously used or processed plastic materials which have been cleaned and reground.

REGRIND: (1) Waste plastics which are recovered and reprocessed for reuse. (2) Plastics which have been ground or pelletized at least twice.

RELIEF ANGLE: (1) The angle of the cutaway portion of the pinch-off blade measured from a line parallel to the pinch-off land. (2) In a mold the relief angle is the angle between the narrow pinch-off land and the cut away portion adjacent to the pinch-off land.

RETAINER PLATE: The plate on which demountable pieces, such as mold cavities, ejector pins, guide pins, and bushings are mounted during molding; usually drilled for steam or water.

RIB: A reinforcing member of a fabricated or molded part.

ROTATIONAL MOLDING: A process used to make hollow plastic parts.

RUNNER: In an injection or trans fer mold, the channel that connects the sprue with the gate to the cavity.

RUNNER SYSTEM: The term usually applied to all the material in the form of sprues, runners and gates which lead material from the nozzle of an injection machine to the pot of a transfer mold to the mold cavity.

SCRAP: A product or material which is out of specification to point of making it unusable.

SHEAR: Stress developed in material due to the action of the layers in the material attempting to glide against or separate in a parallel direction.

SHELF LIFE: An expression to describe the time a thermoset material such as molding compound can be stored without losing any of its original physical or functional properties.

SHORT OR SHORT SHOT: A molded part produced when the mold has not been filled completely.

SHOT: The yield from one complete molding cycle, including cull, runner, and flash.

SHOT CAPACITY: The maximum volume of material which a machine can produce from one forward motion of the plunger or screw.

SHRINKAGE: In a plastic, normally the reduction in dimensions after cooling.

SIDE CORING: SIDE ACTIONS OR SIDE DRAW PINS, (1) An action built into a mold which operates at an angle to the normal open and close action of the mold and is used to facilitate the removal of parts which would not clear a cavity or core on the normal press action. (2) Projections used to core a hole in a direction other than the line of closing of a mold, and which must be withdrawn before the part is ejected from the mold.

SINK MARK: A depression or dimple on the surface of an injection molded part due to collapsing of the sur face following local internal shrinkage after the gate seals. May also be an incipient short shot.

SPECULAR GLOSS: The relative reflective appearance of a material as judged visually.

SPIDER GATE: Multi-gating of a part through a system of radial runners from the sprue.

SPLAY MARK: Marks or lines found on the surface of a part after molding which may be caused by overheating the material, moisture in the material, or flow paths in the part. Usually white, silver, or gold in color. Also called SILVER STREAKING.

SPRUE: Feed opening provided in the injection or transfer mold; also, a slug formed at this hole. Spur is a shop term for the sprue slug.

SPRUE GATE: A passageway through which molten plastic flows from the nozzle to the mold cavity.

SPRUE LOCK OR PULLER: In injection molding, a portion of the plastic composition which is held in the cold slug well by an undercut; used to pull the sprue out of the bushing as the mold is opened. The sprue lock itself is pushed out of the mold by an ejector pin.

SPRUE-BUSHING: A hardened steel insert in an injection mold which contains the tapered sprue hold and has a suitable seat for the nozzle of the injection cylinder. Sometimes called an Adapter.

STATIONARY PLATEN: The plate of an injection or compression molding machine to which the front plate of the mold is secured during operation. This platen does not move during normal operation.

STEAM PLATE: Mounting plate for molds, cored for circulation of steam.

STRESS CRACK: External or internal cracks in a plastic caused by tensile stresses less than its short-term mechanical strength.

STRIATION: (1) A separation of colors resulting in a linear effect of color variation. (2) In blow molding, the rippling of thick parisons. (3) A longitudinal line in a plastic due to a disturbance in the melt path.

STRIPPER-PLATE: A plate that strips a molded piece from core pins or cores.

SUBMARINE GATE: A type of edge gate where the opening from the runner into the mold is located below the parting line or mold surface as opposed to conventional edge gating where the opening is machined into the surface of the mold. With submarine gates, the item is broken from the runner system on opening of the mold or ejection from the mold.

TAB GATED: A small removable tab of approximately the same thickness as the mold item, usually located perpendicular to the item. The tab is used as a site for edge gate location, usually on items with large flat areas.

TAPPING: Cutting threads in the walls of a circular hole.

THREAD PLUG, RING, OR CORE: A part of a mold that shapes a thread.

TIE BARS: Bars which provide structural rigidity to the clamping mechanism of a press and usually guide platen movement.

TOLERANCE: A specified allowance for deviations in weighing, measuring, etc., or for deviations from the standard dimensions or weight.

UNIT MOLD: (1) Mold designed for quick changing interchangeable cavity parts. (2) A mold which comprises only a single cavity, frequently a pilot for the production set of molds.

VACUUM METALIZING: Process in which surfaces are thinly coated with metal by exposing them to the vapor of metal that has been evaporated under vacuum (one millionth of normal atmospheric pressure).

VENT: In a mold, a shallow channel or minute hole cut in the cavity to allow air to escape as the material enters.

VERTICAL FLASH RING: The clearance between the force plug and the vertical wall of the cavity in a positive or semi-positive mold; also the ring of excess material which escapes from the cavity into this clearance space.

VINYL: Usually polyvinyl chloride, but may be used to identify other polyvinyl plastics.

VIRGIN PLASTICS: Material not previously used or processed and meeting manufacturers specifications.

VOID: A void or bubble occurring in the center of a heave thermoplastic part usually caused by excessive shrinkage.

WARPAGE: Dimensional distortion in a plastic object after molding.

WHEELABRATING: Deflashing molded parts by bombarding with small particles at a high velocity.

YIELD VALUE: The lowest stress at which a material undergoes plastic deformation. Below this stress, the material is elastic; above it, viscous.

This guiding article is based on industry-common knowledge and information available on the web. While we strive to provide accurate and useful information, readers are encouraged to cross-reference with additional sources and seek professional advice when necessary. The content here is intended for general understanding and should not replace individualized guidance from experts in the field. We do not take responsibility for any decisions made based solely on the information provided in this article.